Energy Savings

• 1). Subtract the wattage of the CFL from the incandescent bulb replaced. For example, a 23-watt fluorescent gives the same light intensity as a 100-watt incandescent using 77 fewer watts of electricity.
  
  
• 2). Calculate or estimate the total number of hours the CFL is on each month. Multiply by the above sum to get a total number of watt-hours saved. For example if the light is used 10 hours per month, you are saving 770 watt-hours of electricity.
  
  
• 3). Repeat for each incandescent bulb replaced.
  
  
• 4). Sum the total of the watt-hours saved and divide by 1,000 to get the total number of kilowatt-hours (kwh) saved per month.
  
  
• 5). Multiply the number of kwh saved by the cost per kwh listed on your electric bill. If you have five lights that save 770 watt-hours each per month, or 3.85 kwh, the total savings per month for the new bulbs is 38.5 cents if your cost per kwh is 10 cents.
  
  

Bulb Cost

• 1). Determine the cost of the CFL and a comparable incandescent bulb.
  
  
• 2). Multiply the cost of an incandescent bulb by 9, the factor by which the average life span of a CFL exceeds that of an incandescent bulb.
  
  
• 3). Subtract the price of the CFL from the cost of the comparable incandescent bulb to figure savings per bulb. Therefore, if your CFL costs $5 and your incandescent $1, you save $4 for each bulb over the lifetime of the bulb.